# -*- coding: latin-1 -*-
# Copyright (c) 2007-2009 Jorge Ortiz Romo <jortizromo@gmail.com>
#                         Freymam Vallejo Cuero <freturn@gmail.com>
# Permission is hereby granted, free of charge, to any person
# obtaining a copy of this software and associated documentation
# files (the "Software"), to deal in the Software without
# restriction, including without limitation the rights to use,
# copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the
# Software is furnished to do so, subject to the following
# conditions:

# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.

# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
# OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
# HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
# WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
# FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
# OTHER DEALINGS IN THE SOFTWARE.
# Import the module and instantiate a pygraph object


from __future__ import division



def density(valued_graph):
    weight_sum = 0
    edges = []
    tuple_edge = tuple
    for edge in valued_graph.edges():
        edges.append(edge)
        tuple_edge = (edge[1],edge[0])
##        if tuple_edge not in edges:
        weight_sum = weight_sum + valued_graph.edge_weight(edge[0], edge[1])
    num_nodes = len(valued_graph.nodes())
    return weight_sum / ((num_nodes )*(num_nodes-1))
